#include <iostream>
#include <random>
#include <sstream>
#include <iomanip>
#include <string>
#include <atomic>

std::string uuid()
{
    std::random_device rd;
    std::mt19937_64 generator(rd());
    std::uniform_int_distribution<int> distribution(0, 255);
    std::stringstream ss;
    for (int i = 0; i < 8; ++i)
    {
        ss << std::setw(2) << std::setfill('0') << std::hex << distribution(generator);
        if (i == 3 || i == 5 || i == 7)
            ss << '-';
    }

    static std::atomic<size_t> seq(1);
    size_t num = seq.fetch_add(1); // atomic promise thread safe
    for (int i = 7; i >= 0; i--) 
    {
        ss << std::setw(2) << std::setfill('0') << std::hex << ((num>>(i*8)) & 0xff);
        if (i == 6) ss << "-";
    }

    return ss.str();
}

int main()
{
    for (int i = 0; i < 10; ++i)
    {
        std::cout << uuid() << std::endl;
    }

    return 0;
}
